Potentiometer



Nov. 18, 1958 K. H CHAPPLE POTENTIOMETER Filed Sept. 16, 1955 FIG. 4

KENNETH H. CHAPPLE INVENTOR WW ATTORNEY FIG 6 United States Patent POTENTIOMETER Kenneth H. Chapple, Blnghamton, N. Y., assignor to Link Aviation, Inc, Blnghamton, N. Y., a corporation of New York Application September 16, 1955, Serial No. 534,656 9 Claims. (Cl. 201-48) My invention relates to an improved electrical potentiometer, and more specifically, to a means for providing connections'or taps at desired places on the winding of a precision electrical potentiometer. In the analog com puter, automatic control and instrumentation arts, the use of tapped electrical potentiometers for deriving potentials commensurate with shaft rotations is well known, and ganged tapped potentiometers are commonly positioned by servo shafts and the outputshafts of mechanical differentials. Taps are generally provided on such potentiometers in order to connect resistances, diodes or other impedances in parallel with certain sections of the potentiometer winding, or to connect selected potentials to selected points on the winding to effect a desired potential distribution across the winding. The provision of a particular potential distribution pattern along a potentiometer winding is sometimes termed shaping the potentiometer, since it provides a means of obtaining a desired voltage versus shaft rotation characteristic which is sometimes obtained by varying the width or shape of the potentiometer winding. By shaping techniques well known in the art, linear potentiometers may be made non-linear according to a desired function, and the non-linearity of other potentiometers may be altered. One well-known means for providing taps on a precision potentiometer winding is by welding or soldering a wire to the potentiometer winding at a desired point. Since the necessity of providing high resistance in the potentiometer winding dictates that resistance wire of very fine gauge be used in the potentiometer winding, the welding of a tap con- I nection wire to the winding wire is usually an extremely tedious and delicate operation which must be performed by hand and by observation through a strong magnifying glass. Furthermore, it is very desirable in many instances to shift the position of a tap connection of a potentiometer in order to re-scale the computer system, or to compensate for loading errors and for other reasons well known to those skilled in the art. Because of the expense and difficulty attending the welding of potentiometer taps and because of the impossibility of making necessary adjustments to such taps, it has become common to provide potentiometer taps in the form of fixed contacts which bear resiliently against the potentiometer winding in desired locations. A typical example of such an arrangement is shown in U. S. Patent No. 2,606,984, granted Aug. 12, 1952, to L. M. Burgess.

While the device shown in Patent 2,606,984 has received wide use, it has several disadvantages which make it unsuitable for use in particular analog computer, auto matic control and instrumentation applications. Many potentiometers must be provided with a large number of taps in order to eliect a desired potential distribution, and as well as being movable collectively along the potentiometer winding, it is very necessary in certain instances that the potentiometer taps be movable individually with respect to each other. While it is well known that a tap connection in such a prior art potentiometer may be shifted slightly by bending or turning the resilient tap contact, it will be recognized that the range of adjustment by such a procedure is undesirably limited, and that the shifting of a tap contact by bending or turning it about a fixed axis may disturb the contact pressure needed to insure that the tap makes proper electrical contact with the potentiometer winding. Furthermore, in certain instances it is necessary or desirable to increase or decrease the number of tap connections on a particular potentiometer, and it is very desirable that a potentiometer be provided in which taps can be added or subtracted without having to disconnect and re-connect all of the existing tap connections.

It is therefore a primary object of the invention to provide an improved precision potentiometer having individually adjustable taps.

It is an additional object of the invention to provide an improved precision potentiometer having adjustable taps which may be located at many widely-displaced points on avpotentiometer winding and which maintains constant contact pressure on the potentiometer winding regardless of their placement.

It is a further obect of the invention to provide an improved electrical potentiometer in which taps may be easily adjusted relative to each other as well as adjustable collectively with respect to the potentiometer winding.

Other objects of the invention will in part be obvious and will in part appear hereinafter. I

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts, which will be exemplified in the construction hereinafter set forth, and the scope of the invention wil' be indicated in the claims.

For a fuller understanding of the nature and objects 01. the invention reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a plan view of a preferred embodiment of the invention;

Fig. 2 is a section view through IIII of Fig. 1;

Fig. 3 is a plan view of an alternative embodiment of the invention; a

Fig. 4 is a section view through IV-IV of Fig. 3;

Fig. 5 is a detail perspective view showing the manner in which a tap clamp is carried on a T-shaped rail in the preferred embodiment of Figs. 1 and 2;

Fig. 6 is a detail perspective view showing the manner in which a T-shaped slot is utilized in the alternative embodiment of Figs. 3 and 4 to provide readily and accurately adjustable tap mounting means.

Referring now to Figs. 1 and 2 there is shown in plan and section a preferred embodiment of the invention. The improved potentiometer comprises a generally cylindrical housing 10 having an integral end wall 11. Cylinder 10 is commonly provided with annular ridges and shoulders as at 12 and 13, so that a plurality of such potentiometers may be mounted concentrically, with the circular land 12 of one potentiometer fitting snugly in on the shoulder 13 of an adjacent potentiometer. The end wall portion 11 of housing 10 carries a bushing or bearing 14 in which is journalled shaft 16. Insulating sleeve 17 is carried on shaft 16 as shown, serving to insulate rigid clamping arm 18 from shaft 16. Arm 18 is tightly clamped onto shaft 16 by tightening screw 19. Hence it will be seen that rotation of shaft 16 will serve to rotate arm 18. Also mounted concentrically about shaft 16 is a fixed insulating bushing 20 carrying a conductive slip ring 21. Brushes 22 and 23 fastened mechanically and electrically at 24a to arm 18 bear against slip ring 21. A wire connection (not shown) is made between slip ring 21 and one of the terminals 24 mounted on insulating terminal block 25, so that the potential appearing on arm 18 also appears on one of the outside terminals 24. Ann 18 carries a resilient wiper arm 26 which engages resistance winding 27, so that the potential at a particular point on winding 27 is connected via arm 18 to one of the outside terminals carried on terminal block 25. Also carried on arm 18 is a rigid connecting arm 28 which extends parallel to shaft 16, and which is used to rotate the shaft of a successive similar potentiometer. Pin or arm 28 may be either a conductive or non-conductive material, but it is important that it be rigid, in order to avoid backlash between the two Potentiometers. Those skilled in the are will recognize that the parts of Figs. 1 and 2 described thus far are completely conventional. Also, while a wirewound resistor has been shown, it will be apparent that the invention is applicable as well to filmtype potentiometers.

concentrically mounted on the end wall portion 11 of cylindrical housing is an annular T-shaped ring 30 formed of Micarta, fiber, or a like insulating material, which ring provides a rail or track around which adjustable taps may be disposed. Ring 30 is fastened to end wall 11 as by means of nylon insulating screws 31, 31 or a suitable adhesive and a cutout portion is provided as at 32 to allow the installation and removal of adjustable tap contacts when ring 30 has been installed in position on end wall 11. As best seen in the detail view of Fig. 5, adjustable tap-contact clamps such as 33 are carried on rail 30, with the edges 34, 35 of clamp 33 surrounding the flange 36a of rail 30. Clamp 33 may be seen to comprise a segment of ring which is a hollow box-shape in cross-section with a slot provided in its lower side to accommodate web portion 37 of rail 30. Clamp 33 is preferably formed by cutting segments from a ring of proper cross-section so that the clamp will fit snugly on rail 30 and will slide along rail 30 without rocking or rotating about its own axis. It will be seen that the arc length of gap or cutout portion 32 of rail 30 is determined by the arc width of the clamps to be utilized in the potentiometer, and it is advantageous to locate the cutout portion of rail 30 directly radially inwardly from the ends 27a, 27b of resistance winding 27 so that taps may be located at any radial position along the winding. Set screw 36 is threaded through the top of clamp 33, so that turning of screw 36 will lock clamp 33 in a selected position on rail 30. Afiixed to each clamp as by means of soldering or welding is a resilient tap arm (such as 38 in Fig. 5), which may comprise a small piece of sheet metal bent to the desired shape. The base portion 39 of arm 38 is seated on the fiat top surface of clamp 33, and a hole (not shown) in arm 38 permits threading of set screw 36 into clamp 33. Arm 38 carries a precious metal contact 40 which is urged outwardly against the resistance winding by the resiliency of arm 38. Since the resistance winding is concentrically installed in the potentiometer, it will be seen that as clamp 33 is moved along track 30 to various positions, that the radially acting spring force on arm 38 will remain the same, insuring that ample contact pressure will be maintained between contact 40 and the resistance winding. Also, because clamp 33 fits snugly on rail 30 v and is constrained against rotating, the contact pressure between arm 38 and clamp 33 cannot result in contact 40 becoming mis-adjusted as in prior art otentiometers of this type. Even if screw 36 were to loosen slightly, since the force from spring arm 38 acts radially on clamp 33 there is no tendency to slide clamp 33 along rail 30, and hence contact 40 will remain in contact with the same turn or turns of the resistance winding. A small ear 41, to which a Wire connection (not shown) may be connected to one of the terminals of terminal block 25.

As well as the symmetrical type of spring arm shown in Fig. 5, spring arms may be provided in left-hand and right-hand types as shown at 43 and 44 in Fig. I. It will be seen that if only symmetrical spring arms such as 38 were used, that the minimum allowable spacing between.

a pair of adjacent taps would be governed by the widths of theirv rail-gripping clamps, since a small gap must be maintained between adjacent clamps to prevent shorting together'adjacent taps. However, it will be seen that by use of rightand left-hand offset or circumferentially extending spring arms such as 43 and 44, that adjacent taps may be set very close to each other while maintaining ample spacing between their respective clamps. It will be seen that if the wire connection between each tap assembly and terminal block 25 is of sufiicient length, that additional taps may be added with case, since existing tap assemblies may be temporarily removed merely by loosening their set screws and sliding them around to cutout portion 32, and taps to be added may be inserted between existing taps if desired, as well as near the ends of the potentiometer winding.

Shown in Figures 3, 4 and 6 is an alternative embodiment of the invention in which the tap-carrying track 45 comprises a slotted annular channel of insulating material, having inwardlyprotruding edges 51 and 52. The contact-carrying spring arm 46 comprises a flat portion 47a which may be located in position on track 45 by means of screw 53. Screw 53 threads into nut 54 carried inside track 45. A cutout portion 47 of track 45 provides an opening at which nuts (not shown) for additional tap assemblies may be inserted into the track. In order to insure that the spring force of arm 46 does not cause the arm to rotate and mis-adjust the potentiometer, a pair of ears (one of which is shown at 48) on arm 46 seat against the outside edge of the track, and a pair of ears 55, 56 seat against the inside of the track. A solder terminal 50 is provided on arm 46 to make a wire connection to the potentiometer terminal block. As seen in Fig. 3, the tap-contact springs of this embodiment of the invention may also be made in left-hand and right-hand types as shown at 57 and 58, so that extremely close tap spacing may be obtained if desired. Inasmuch as the other parts of the embodiment of Figs. 3 and 4 may be identical to those of Figs. 1 and 2, further description of the alternative embodiment is deemed to be unnecessary. The embodiment of Figs. 1, 2 and 5 is preferred to the alternative embodiment principally because the T- shape track 30 may be molded or otherwise fabricated at less expense than the more complex channel track 45, and because the clamps of the preferred embodiment may be locked in place with greater ease. The alternative embodiment, however, utilizes a one-piece clamp-spring arm which may be locked in place with merely a screw and a nut, so that no soldering or welding of the spring arm to a separate clamp is necessary. If desired, track 45 of the alternative embodiment may be made in two separate channel-shaped pieces as indicated by line 59 in Fig. 6, or in other paired shapes which provide a T- slot in order to simplify the fabrication of the track.

While I have shown the invention applied to a specific potentiometer, those skilled in the art will readily recognize in light of this disclosure that the invention may be applied to many other potentiometers.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained, and since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

. Having described my invention, what I claim as new and desi e lo secure by Letters Patent is;

able along said track, and means to lock said spring arm at a fixed position along said track.

2. In a rotary potentiometer having a cylindrical housing provided with an end wall, a circular resistor mounted within said housing and a rotatable contact engaging said resistor, the combination of an annular insulating track mounted concentric with said resistor, a resilient arm mounted on said track, said resilient arm carrying an electrical contact and, urging said contact radially against said resistor, said arm being continuously slidable along said track, and means to lock said arm at any selected location on said track.

3. Ina rotary potentiometer having a cylindrical housing provided with an end wall, a circular resistor mounted within said housing and a rotatable contact engaging said resistor, the combination of an annular insulating track mounted on said end wall concentric with said resistor, a resilient arm slidably mounted on said track, said resilient arm carrying an electrical contact and urging said contact radially against said resistor, and means for maintaining the force of said resilient arm in a radial direction.

4. In a rotary potentiometer having a cylindrical housing provided with an end wall, a circular resistor mounted within said housing and a rotatable contact engaging said resistor, the combination of an annular insulating track having a T-shaped cross-section mounted concentric with said resistor, a clamp carrying a resilient arm slidably mounted on said track, an electrical contact mounted on said arm and urged radially against said resistor by the resilience of said arm, and a set screw carried in said clamp to lock said clamp in a fixed position on said track.

5. In a rotary potentiometer having a cylindrical housing'provided with an end wall, a circular resistor mounted within said housing and a rotatable contact engaging said resistor, the combination of an annular insulating track having a T-shaped cross-section mounted concentric with said resistor, a clamp surrounding the upper portion of the T-shape of a segment of said track slidably mounted on said track and carrying a resilient arm, and an electrical contact mounted on said arm and urged radially outward to engage said resistor.

6. In a rotary potentiometer having a cylindrical housing provided with an end wall, a circular resistor mounted within said housing and a rotatable contact engaging said resistor, the'combination of an annular insulating track having a T-slot in cross-section mounted concentric with said resistor, a resilient arm'carried on said track, said arm carrying-an electrical contact and urging said contact radially outward against said resistor, a lock screw and a nut for locking said arm in a selected position along said track, said nut being carried within said T-slot of said track.

7. A potentiometer according to claim 6 in which said resilient arm has a plurality of projecting portions which bear against said track to constrain said arm against rotation.

8. In a rotary potentiometer having a cylindrical housing provided with an end wall, a circular resistor mounted within said housing and a rotatable contact engaging said resistor, the combination of an annular insulating track having a T-shape in cross-section mounted concentric with said resistor, a clamp having a T-slot registrable with said T-shape slidably mounted on said track and carrying a resilient conductive arm, an electrical contact mounted on said arm and urged radially outwardly to contact said resistor, and a wire connection between said arm and terminal mounted on the exterior of said housing.

9. In a rotary potentiometer having a cylindrical housing provided with an end wall, a circular resistor mounted within said housing and a rotatable contact engaging said resistor, the combination of an annular insulating track mounted concentric with said resistor, a plurality of resilient arms slidably positioned at selected places along said track, each of said arms carrying an electrical contact and urging said contact radially outward against said resistor, at least one of said arms extending circumferentially as well as radially, whereby the contact carried by said one of said arms may be positioned in close proximity to the contact carried by a second of said arms while maintaining substantial separation between said one arm and said second arm.

References Cited in the file of this patent UNITED STATES PATENTS 1,875,078 McArdle Aug. 30, 1932 2,093,358 Holler Sept. 14, 1937 2,144,216 Broome Jan. 17, 1939 2,551,989 Wilson May 8, 1951 2,606,984 Burgess Aug. 12, 1952 2,619,570 Takats Nov. 25, 1952 FOREIGN PATENTS 658,123 Great Britain Oct. 3, 1951 1,056,757 France Oct. 28, 1953 

